A description is given, using a coal-burning boiler furnace as an example of the soot blower-installed equipment. Since a combustion gas for a coal-burning boiler furnace contains a great deal of ash, ash is likely to adhere to the surface of the members disposed inside the boiler furnace, and in particular, ash adheres to the outer surface of heat transmission tubes disposed in the boiler furnace. Further, adhering ash is deposited in layers.
FIG. 10 is a view showing a general construction of the inside of the boiler furnace 1. As shown in FIG. 10, a group 3 of suspension type heat transmission tubes is installed on the ceiling of the boiler furnace 1, and a group 4 of horizontally installed heat transmission tubes are disposed on the rearward heat transmission section. The group 3 of suspension type heat transmission tubes and the group 4 of horizontally installed heat transmission tubes are, respectively, composed of a number of heat transmission tubes, and the surfaces of these groups 3 and 4 of heat transmission tubes are in contact with a high temperature combustion gas containing combustion ash.
Therefore, combustion ash adheres to and accumulates at (hereinafter, adhesion and accumulation are merely called “adhesion”) the surfaces of heat transmission tubes that constitute these groups 3 and 4 of heat transmission tubes. If the combustion ash excessively adheres to the surfaces of the above-described heat transmission tubes, heat transmission of water or steam fluid, which flows from the high temperature combustion gas to groups 3 and 4 of the heat transmission tubes, is hindered to lower the capacity of a boiler apparatus. Also, the greater the amount of ash that adheresto the above-described heat transmission tubes, the greater the waste combustion gas temperature becomes, which is expelled from the boiler furnace 1.
Therefore, a soot blower that is installed inside a boiler furnace 1 is usually operated periodically (a steam injection type soot blower has frequently been employed) in order to blow out combustion ash that adheres on the surface of the above-described heat transmission tubes, whereby the heat transmission capacity is prevented from lowering.
Recently, a sonic soot blower 6, in which sonic waves are utilized, shown in FIG. 10 has been applied to a boiler apparatus. A plurality of sonic soot blowers 6 is installed on the furnace wall at portions where groups 3 and 4 of heat transmission tubes of the boiler furnace 1 are installed.
The sonic soot blowers 6 oscillate sonic waves of high sonic pressure to a space surrounded by the furnace wall of the boiler furnace 1 and vibrate a combustion gas, etc., wherein minute displacement is given to the combustion ash that has adhered to the surfaces of the respective heat transmission tubes of groups 3 and 4 of the heat transmission tubes, and the combustion ash is finally dropped from the surfaces of the heat transmission tubes. In addition, in the process of oscillating the above-described sonic waves, there is another effect by which combustion ash is prevented from adhering to the surfaces of the heat transmission tubes.
The sonic soot blower 6 includes a sonic wave oscillator, in which an oscillation plate oscillates sonic waves by using high pressure air, etc., a resonance tube that resonates the sonic waves oscillated by the corresponding sonic wave oscillator at a specified frequency, and a horn to amplify them. The sonic soot blower 6 oscillates said amplified sonic waves into the boiler furnace 1 and forms stationary waves by exciting columnar oscillations in the boiler furnace 1 with the sonic waves. By heightening the sound pressure in the furnace 1 with the corresponding stationary waves, combustion ash adhered to the surfaces of the heat transmission tubes is removed and is thus prevented from adhering to the heat transmission tubes.
Since the combustion gas temperature changes due to an operation load of the boiler in the boiler furnace 1, the columnar resonance frequency in the furnace changes. In order to effectively remove ash by using the sonic soot blower 6, it is necessary to maintain the in-furnace columnar resonance required regardless of the operating conditions of the boiler. However, since the oscillation frequency of a sonic wave oscillator used in a prior art sonic soot blower 6 is constant, the in-furnace columnar resonance is established only when the gas temperature conditions in the furnace correspond to the above-described transmission frequency, wherein the sound pressure is increased in the furnace, and the effect of removing ash is increased. When no in-furnace columnar resonance is established as the temperature conditions of the exhaust gas in the furnace changes, the sound pressure is lowered, and the effect of removing ash is greatly reduced. Therefore, the prior art soot blower 6 had a problem in that it could not be operated satisfactorily in a wide range of operating conditions of a boiler.
Accordingly, it is the first object of the invention to enable a sonic soot blower to function in a wide range of operating conditions for soot blower-installed equipment such as a boiler by varying the sonic wave oscillation frequency by a simple method.
Also, where the sonic soot blower 6 is installed at the furnace wall of, for example, a boiler furnace 1, no sound pressure distribution in the furnace width direction of the boiler furnace could be confirmed when stationary waves occurred in the boiler furnace 1 by the sonic soot blower 6 are formed, and no stationary waves could also be confirmed. The reason is that a sound pressure level measurement microphone cannot be inserted into the inside of the boiler furnace because the inside of the boiler furnace is at a high temperature during the operation thereof. In addition, even if the sound pressure detector secured at the furnace wall of, for example, the boiler furnace 1 can measure the sound pressure level, only the sound pressure level on the furnace wall can be measured, wherein it is impossible to discriminate whether it was the sound pressure when the stationary waves could be formed or when the stationary waves could not be formed.
The second object of the invention is to enable the confirmation of the stationary wave frequency of the sonic waves inside the corresponding apparatus when operating the sonic soot blower in the soot blower-installed equipment, to enable the control of removal of powdery dust, etc., on the members that constitute the soot blower-installed equipment, to prevent powdery dust, etc., from adhering to the above-described members.
Further, some of the sonic soot blowers 6 installed on the wall surface of a boiler furnace 1 have an opening whose diameter is approx. 500 mm. The above-described opening provided at the furnace wall is shaped so that a gas flow from the inside of the furnace is piled up. The coal-burning boiler furnace contains much powdery dust such as ash in a gas produced by burning of coal, etc. Therefore, if a coal-burning boiler has been operated for a long period, coal ash invades the inside of the sonic soot blower through the above-described opening and accumulates and may close the above-described opening. Further, the temperature of the casing, in which a sonic wave oscillator of the sonic soot blower and a horn thereof are accommodated, increases due to radiant heat of a high temperature gas, and a problem arises in the strength of the corresponding casing.
Also, since there are many cases in which the sonic soot blower 6 is installed on the wall of a boiler furnace, the sonic soot blower 6 is cooled down (the boiler furnace 1 is operated in a reduced pressure level less than the atmospheric air for safety) by compressed air being sucked into the furnace 1 through the above-described opening via the sonic soot blower. It is necessary to attach approximately 30 units of sonic soot blowers 6 to a large output coal-burning boiler. As the number of sonic soot blowers 6 installed increases, the capacity of a compressor for compressed air increases accordingly, and suction of a great deal of compressed air becomes a factor of disturbance for the control of oxygen concentration in the boiler furnace 1. In addition, if the temperature of compressed air for cooling is lower than the temperature of fluid (such as water, steam or their mixture) in the heat transmission tubes installed in the furnace 1, the above-mentioned fluid that is being heated is cooled.
The third object of the invention is to develop and provide a means for easily cooling the inside of the accommodation casing of the sonic soot blower, to cool the accommodation casing itself of the sonic soot blower and to prevent powdery dust such as ash from adhering to the opening of the furnace wall which the sonic soot blower faces.
Further, where the sonic soot blower 6 is installed on the wall surface of the boiler furnace, the following problems are observed.
Although the combustion gas temperature in the boiler furnace 1 near the position where the sonic soot blower 6 is installed is 300 through 400° C., the pressure in the furnace 1 is adjusted to be lower (by −100 through −50 mmAq) than the atmospheric pressure for the safety when operating the furnace. Therefore, the high temperature in-furnace gas does not flow in the sonic soot blower 6 whose pressure is less than the atmospheric pressure. However, where a difference in pressure between in the furnace 1 and in the sonic soot blower 6 is removed when stopping the operation of the boiler, and the gas temperature in the sonic soot blower 6 is remarkably lower than the in-furnace gas temperature (immediately after the boiler operation stops), humidity (or water) in the gas constituents begins condensing in the sonic soot blower 6. Therefore, drain containing highly corrosive constituents adheres to the inner wall in the sonic soot blower or members installed in the sonic soot blower 6, resulting in corrosion of these inner walls and/or members.
In particular, if devices in the casing in which a sonic wave oscillator equipped with a frequency-regulating portion consisting of accurate mechanical components incorporated is corroded even a little, the frequency-regulating portion will malfunction and cause the operation of the sonic soot blower 6 to stop.
The fourth object of the invention is to provide a countermeasure to prevent dirty gases in soot blower-installed equipment from entering the sonic soot blower.
Also, soot blower-installed equipment to which a sonic soot blower is applied is provided with a plurality of member stages. If the equipment is located in an area where gases containing dust such as ash flow, the accumulation of the dust such as ash may be quickened unless dust such as ash is effectively removed to prevent it from adhering to the plurality of member stages.
The fifth object of the invention is to effectively remove powdery dust such as ash from the soot blower-installed equipment in which a plurality of member stages are provided and to which dust such as ash may likely adhere, and/or to prevent adherence of powdery dust such as ash.